Magnetic pressure liquid circuit breaker



April 30, 1968 H. P. FURTH 3,381,248

MAGNETIC PRESSURE LIQUID CIRCUIT BREAKER Filed Oct. 23, 196E J2 1:]! gl:

I 1 1 I I LII I I II 59 55 INVENTOR.

HAROLD P F (/1? TH 5296;. 5: ynfl 41 9 45 ,arroelvek United StatesPatent 3,381,248 MAGNETIC PRESSURE LIQUID CHRCUIT BREAKER Harold P.Furth, Berkeley, Calif. Filed Oct. 23, 1965, Ser. No. 593,370 1 Claim.(Cl. 335-51) ABSTRACT OF THE DISCLOSURE The present invention relates toa magnetic circuit breaker for breaking the electrical circuit between apair of electrically conductive liquids. A magnetic field generated by acoil in the vicinity of the liquids interacts with current induced inthe liquids to generate magnetic pressure which forces apart the liquidsthereby breaking the electrical circuit.

This invention relates to electrical current circuit breakers and moreparticularly to devices and methods for rapidly interrupting an electriccurrent in a liquid by magnetic pressure.

The increasing use of electrical circuits carrying large currents andhigh voltages has dictated the need for more efficient switchingcircuits. In a copending application entitled, Liquid Level CurrentCircuit Breaker, filed on July 26, 1965, Serial No. 474,762, nowabandoned, by Harold P. Furth, there is disclosed an electrical currentcircuit breaker which utilizes magnetic pressure to interrupt a currentcircuit between a solid electrode and a conducting liquid. Such acircuit breaker offers many advantages over the prior art includingextremely fast operation and ability to switch large currents of highvoltages. While the above mentioned circuit breaker offers manyadvantages over the prior art, certain problems are created by theaction between the solid electrode and the liquid metal conductor. Thereis a tendency to are during the switching which erodes the ends of thesolid electrode. Since the switching may occur at a very high frequency,the surface of the solid electrode is eventually eroded to the point ofrequiring replacement. Accordingly it is an object of this invention toprovide a circuit breaker for opening a current circuit in a fast timewithout erosion of the electrodes.

The device of this invention overcomes the problem of erosion of theelectrodes by interrupting a current between a pair of liquid metalelectrodes. Magnetic pressure of extremely large force instantaneouslyforces the liquid metal electrodes apart to break the current circuit. Afast interruption of a large current high voltage circuit is realizedwithout arcing sufficient to cause any serious erosion during continuousoperation.

It is therefore another object of this invention to provide an improvedelectrical circuit breaker activated by magnetic pressure.

It is still another object of this invention to provide a means forbreaking the electrical circuit between a pair of liquid conductors.

It is a further object of this invention to provide a circuit breakerwhich is not subject to arcing.

It is a still further object of this invention to interrupt a currentbetween a pair of liquid conductors by creating a magnetic field whichreacts to generate magnetic pressure to break the circuit between theconductors.

Other objects and advantages of the present invention will becomeapparent from the following description and appended claims.

In the drawing:

FIGURE 1 is a view of a circuit breaking switch according to a preferredaspect of the invention.

FIGURE 2 is a partial view of the switch of FIG. 1

Patented Apr. 30, 1968 showing the position of the liquid when magneticpressure has been applied to open the circuit.

FIGURE 3 is a view of a second aspect of the invention in which thepulse generating coils are located outside of the main switch.

FIGURE 4 is a view of the device of FIG. 3 when magnetic pressure hasbeen applied.

FIGURE 5 is a view of another aspect of the invention in which the pulsegenerating coils are located above the liquid only.

FIGURE 6 is a view of the device of FIG. 5 in open condition.

According to a principal aspect of the invention an electrical currentflowing between liquid metal electrodes is interrupted by magneticpressure which forces the liquid apart. A liquid metal pool is separatedinto a pair of electrodes by an insulating bridge with current flowingbetween the electrodes during the closed position of the switch. A pairof interrupter coils are mounted in relationship with the electrodeswith magnetic pressure generated by activation of the coils forcing theliquid electrodes apart during the open position of the switch.

Before proceeding to a detailed description of the device of theinvention a brief discussion of the principles defining the operation ofthe device of the invention will be made. As described in the copendingapplication referred above, a rapid displacement of liquid metal can beaccomplished by pulsing on a magnetic field of strength B in a coil atthe surface of the liquid metal. The pulse risetime is made sufiicientlyshort so that the associated skin depth in the liquid metal is smallerthan the dimension of the region of liquid metal that is to bedisplaced. The pulsed magnetic field is effectively excluded from thevolume of the liquid metal and exerts a pressure B /S on r the surfaceof the liquid. If B is expressed in gauss, then where V is the massdensity of the metal and T is in seconds. If D is, for example, .5 cm.and B is 25,000 gauss and if the liquid metal is sodium, with V=1 gm./0111. then the time is sec. The skin depth in liquid sodium for t=l00sec. is .3 cm., so it may be readily seen that the pulsed magnetic fieldis in fact effectively excluded from the volume of the liquid metal. Itis this principle of interaction between a magnetic field and the skinof a liquid metal which produces magnetic pressure to force liquidelectrodes apart and break the current circuit between them.

Referring now to the drawing and in particular to FIGS. 1 and 2 there isillustrated a principal aspect of the invention. In FIG. 1 a pair ofliquid metal electrodes are produced by the structure including an outerliquid metal pool 16 and an inner liquid pool 14 which are suitablyenclosed by a casing 17. The pools 14 and 16 are separated by insulatortubes 21 having coils 19 mounted thereon. The coils 19 are suitablylocated a short distance below the level of the pools 14 and 16 so thatduring the position of the switch when current is flowing between thepools 14 and 16 current flows through the bridge 15, which is thatportion of the liquid above the coils 19 between the pools 14 and 16.The switch includes a solid center electrode 13 which is connected to aterminal 11 responsively connected to the initial source of current. Thelower end of the electrode 13 is immersed in the inner liquid pool 14and suitably insulated from the outer casing 17. The terminal 12completes the current path by being conductively connected to the outercasing 17 which is a metallic conductor. Thus when the circuit is in theclosed position, current fiows from the terminal 11 through Locatedabove the tubes 21 and coils 19 are corresponding tubes 20 and coils 18which interact with the coils 19, in a manner to be described to providethe magnetic pressure for forcing the liquid pools 14 and 16 apart. Thecoils 18 and 19 are mounted in close relationship so that the coils 18are just above the level of the pools 14 and 16 and the coils 19 arejust below the level of the pools. Electrical pulse current for thecoils 18 and 19 is provided by a suitable source of high voltage largecurrent, through corresponding leads 22 for the coils 18, and leads 23for the coils 19. It is to be noted that the level of the pools 14 and16 is slightly depressed as illustrated in FIG. 1 during operation whichis caused by the magnetic pressure exerted during the flow of currentthrough the center electrode 13 when the circuit is completed.

Turning now to the operation of the device of FIG. 1 when the circuit isinterrupted, as shown in the partial view of FIG. 2, current isinterrupted between the liquid pools 14 and 16 by magnetic pressuregenerated by the interaction between the magnetic fields created by thecoils 18 and 19 and the current flowing on the surface of the pools 14and 16. A current pulse of high magnitude in the coils 18 and 19generates magnetic fields whose lines of force are illustrated in FIG.2. The current in the coils 18 produces lines of force shown by thelines 24 and the current in the coils 19 produces lines of force 25. Theinteraction between these lines of force and the current induced in theskin of the pools 14 and 16 in the vicinity 15 generates magneticpressure. This pressure forces the liquid pools apart thus breaking thebridge 15 as shown in FIG. 2. Since the device is cylindrical instructure, the pools 14 and 16 are completely electrically separated byreason of the magnetic force in the region of the bridge 15.

Electrical arcing during the interruption of current between the pools14 and 16 is greatly minimized by reason of the separation between apair of liquid electrodes as opposed to the prior art devices whereinsolid electrodes were used. Additionally arcing between the liquid pools14 and 16 and the coils 18 and 19 is greatly reduced by the action ofthe magnetic lines of force. As seen in FIG. 2 the lines of force 24 and25 have horizontal components which act to force the liquid pools 14 and16 apart at the bridge 15 and vertical components which tend to causeany radial are generated to be rapidly elongated thereby extinguishingthe arc. This is realized since the radially outer part of the arc willmove in the opposite azimuthal direction from its radially inner part.In that event the opposite direction movement of the lines of force 24and 25 elongate the arc thereby extinguishing it.

To further prevent arcs from being generated dun'ng the interruption ofcurrent between the pools 14 and 16 there is included a high pressuregas, such as argon, within the casing in the region 30 above the pools14 and 16.

In order to further minimize arcing, a layer of oil may be placed on thesurface of the pools 14 and 16. The combination of the methods describedabove elfectively eliminate any erosion of the solid parts of the devicefrom arcing thereby contributing to a long life for the device. Themagnetic field, as shown in FIG. 2, causes any arcs to move in adirection orthogonal to the initial are current and the magnetic fieldvector. Since the magnetic field vector is in two directions along thelength of the are as seen by the arrows 32 and 33, for example, thelocal arc velocity will also change its sign thereby distorting andelongating the arc.

In FIGS. 3 and 4 there is illustrated another aspect of the invention inwhich a pair of coils 41 and 42 are located outside of the casing 43 ofthe device. The central solid electrode 44 is formed in a diamond shapeto facilitate the parting of the liquid during the interrupting phase.As seen in FIG. 4 when coils 41 and 42 are energized, the region 46joining the liquid electrodes 47 and 48 becomes void of liquid due tothe magnetic pressure which forces the liquid away. The liquid movesaway from the point 49 on the edge of the solid electrode 44 therebytending to suppress any arcs. Similarly the region in the vicinity ofthe coil 42 has its liquid forced away by the generated magneticpressure.

Another aspect of the invention is illustrated in the drawing in FIGS. 5and 6 which show a device in which liquid is separated in two regions bythe action of two coils displaced above the liquid level. The coils 51and 52 located on either side of the central solid electrode 53 eachproduce a force to separate the liquid in a pool 55 in the regions 56and 57 where insulating tubes 58 and 59 extend from the bottom of thepool to a position just below the level of the liquid pool.

The liquid level current interrupting device of the invention provides adistinct advantage over other circuits by utilizing a pair of liquidelectrodes as the contacting electrodes. Arcing is almost eliminatedthereby producing an extremely long life for the device. Additionallythe magnetic pressure operation produces a tremendously fast ispractically nonexistent due to the presence of liquid switching time inthe operation of the device. Overheating electrodes.

While the invention has been disclosed herein with respect to theembodiments illustrated in the drawing, it will be readily apparent thatnumerous variations and modifications may be made within the spirit andscope of the invention. For example, as previously described, a numberof different locations for the current coils may be utilized to producethe most eifective magnetic pressure on the liquid conductors.

I claim:

1. In a circuit breaker, the combination comprising:

a liquid metal enclosed in a metallic casing,

insulating means in said casing for separating said liquid metal intoinner and outer pools,

said insulating means extending to a height just below the surface ofsaid pools to form a bridge region between said pools,

means for applying current to said metal casing and said liquid metal toprovide a circuit between said inner and outer pools through said bridgeregion,

and means for generating magnetic pressure in said bridge region toforce said liquid apart in said bridge region,

said means for generating magnetic pressure comprising a pair of coilsin said bridge region, one of said coils above the liquid level, and theother said coil below said liquid level, and means for pulsing saidcoils to 4/1895 Lernp 33550 1/1911 Lohr 200l52 BERNARD A. GIL'HEANY,Primary Examiner.

H. BROOME, Assistant Examiner.

